The present invention relates to a vehicle tire, especially for motorized vehicles, with a device for generating data for further determination of actual frictional conditions between the footprint of the vehicle tire and the road surface on which the tire is running tire-road adhesion, whereby the device is substantially comprised of a plurality of individual magnetic sensor elements that cooperate with one another and a magnetic field positioned radially to the individual sensor elements. The magnetic sensors comprised of a group of individual sensor elements are connected to an evaluation device.
Such a vehicle tire is, for example, known from German patent 39 37 966. In this document a method for determining the frictional conditions (tire-road adhesion) between the vehicle tire and the road surface is disclosed whereby at one or more measuring locations within the tire local deformations, resulting within the footprint when the tire rolls on the road surface, are detected in a horizontal direction as well as in the normal direction at the footprint. Based on the localized deformations, the normal forces and the horizontal forces are determined and the frictional coefficient (tire-road adhesion coefficient) as a ratio of the horizontal force to the normal force is determined.
The friction between the vehicle tire and the road surface, i.e. the tire-road adhesion, ensures the transmission of acceleration forces and lateral guiding forces. The maximum frictional coefficient determines the limits of a stable driving behavior of the vehicle. Thus, it is important for maintaining a stable driving behavior, that the current frictional coefficient remains always below the maximum frictional coefficient. The frictional coefficient is the ratio of the horizontal forces, acting parallel to the road surface, to the vertically acting normal force. For assessing the frictional conditions in the circumferential direction of the tire and in the transverse direction, the frictional coefficient can be divided into a circumferential component, i.e., a longitudinal component, and a transverse component.
Due to the elasticity of the tire material the detected local deformations within the tire can provide data for the respective forces that cause this deformation. With sufficient precision it is thus possible to employ the forces introduced into the tire by the road surface for determining directly the frictional coefficient.
The prior art vehicle tire is provided in the area of the tread strip with at least one magnetic sensor which determines the local deformations and sends measured signals to an evaluation device via a corresponding signal transmission device. For the detection of the local horizontal or vertical stress, elongation, and deformations within the tread lug. Different constructive embodiments are disclosed with regard to the tire in German patent 39 37 966.
For example, permanent magnets are embedded within the tread lugs which change their position depending on the deformation caused by the road surface. Sensors may be connected to the belt ply which respond to the distance changes to the magnets. In this embodiment, the sensors must be securely connected to the belt because their position changes must be reproducible in a defined and reliable manner. The magnets within the tread lugs as well as the sensors within the belt, however, change their relative position during tire manufacture, especially during vulcanization and dishing. Since it is not predictable how this relative position of the two components will change within the finished tire, it is necessary to calibrate each finished tire. This requires high expenditures for their manufacture and the tires are correspondingly expensive. Also, errors made during calibration will make measured results useless.
According to a further embodiment, a sensor pin extends through the tire carcass into the tread lug of the tire tread. The sensor pin comprises four permanent magnets at its end projecting into the interior of the tire. These permanent magnets function as senders. The sensor housing is anchored with pins within the carcass and carries as receivers, for example, four Hall generators. The stress, elongations, and deformations cause a proportional pivoting, respectively, lifting movement of the sensor pin supported within the carcass and thus a distance change between the magnets, respectively, their magnetic field and the Hall generators. Thus, a change of the Hall voltage is the result which is transmitted as a measured signal to the evaluation device. This prior art tire, however, requires an even more expensive construction. Due to the magnets being embedded within the tread lug, whose movement must be detected by the Hall and/or magnetoresistive sensors, it is necessary to introduce at least two structural components into the tire. In addition to the costs for the respective components, the manufacture of the tire itself is also expensive.
It is therefore an object of the present invention to simplify the construction of the vehicle tire of the afore mentioned kind.